The skyline of Philadelphia is seen behind a US Airways Express aircraft at Philadelphia International Airport on Nov. 25, 2010. / Ben Mutzabaugh, USA TODAY

by Ben Mutzabaugh, USA TODAY

by Ben Mutzabaugh, USA TODAY

A multibillion dollar expansion and modernization plan for Philadelphia's delay-plagued airport has taken a crucial step forward after local parties reached a tentative deal, seemingly resolving a years-long impasse that had stalled the effort.

The parties announced the agreement Monday. Still, hurdles remain before the tentative deal becomes a permanent one. Among those hurdles: concern from airlines about the cost of the plan.

The Associated Press writes "the expansion is designed to make one of the nation's busiest airports more competitive by reducing delays and adding capacity and services. Expected improvements include an extra runway, an automated people mover and a new ground transportation center over the next 12 to 15 years."

The plan proposes adding a fifth runway and lengthening two existing runways. The project would cost $6.4 billion based on early estimates, though airport officials say that number could change.

Indeed, it's the cost that has some of the airport's airline tenants worried.

The Philadelphia Inquirer writes Philadelphia's "airlines, which would foot much of the expense, contend the price would be much higher, about $10.5 billion, and could force them to reduce operations in Philadelphia."

US Airways, which is in the process of merging with American, operates one of its largest hubs at the airport. It says it supports some - but not all - of the plan.

American spokesman Todd Lehmacher tells the Inquirer "we remain concerned about the cost of the Capacity Enhancement Program, and continue to question whether a new runway is needed now or in the future."

UPS also has a large presence at Philadelphia International and has expressed its own concerns with the plan, which would require the cargo and shipping company to move its operation to a new location at the airport.

The companies also question whether the project would improve on-time operations at Philadelphia, which frequently sees delays even during minor weather events.

At least in part, those those delay issues come from the tight spacing of the airport's two primary runways, something that often reduces the Philadelphia's arrival rate during less-than-ideal conditions. Still, American/US Airways and UPS each say the congested Northeast airspace is the primary driver for Philadelphia's delays.

"As we and other carriers have noted in the past, delay issues at PHL are the product of airspace congestion, not runway capacity," UPS spokesman Mike Mangeot says to the Inquirer.

Regardless, Philadelphia aviation officials lauded the breakthrough that restarts the city's expansion effort for the airport, which handled nearly 31 million passengers and more than 400,000 takeoffs and landings last year, according to AP.

"Philadelphia is one of America's premier cities, and a premier city needs a premier airport," Philadelphia Mayor Michael Nutter says in a statement announcing the tentative agreement. "The expansion of the airport will mean regional growth, which means more jobs and economic opportunities for residents in the region."